Indole is one of the most abundant heterocycles in bioactive natural products and pharmaceutical agents. Not surprisingly, numerous efforts have been devoted to the preparation of indoles from a diverse range of starting materials. For recent-reviews on indole synthesis, see: (a) Barluenga, J.; Rodriguez, F.; Fananas, F. J. Chem. Asian J. 2009, 4, 1036. (b) Taber, D. F.; Tirunahari, P. K. Tetrahedron 2011, 67, 7195. (c) Vicente, R. Org. Biomol. Chem. 2011, 9, 6469. (d) Platon, M.; Amardeil, R.; Djakovitch, L.; Hierso, J.-C. Chem. Soc. Rev. 2012, 41, 3929. For recent examples of indole annulations, see: (a) Cui, X.; Li, J.; Fu, Y.; Liu, L.; Guo, Q.-X. Tetrahedron Lett. 2008, 49, 3458. (b) Oda, Y.; Hirano, K.; Satoh, T.; Miura, M. Org. Lett. 2012, 14, 664. (c) Ackermann, L.; Lygin, A. V. Org. Lett. 2012, 14, 764. (d) Inamoto, K.; Asano, N.; Nakamura, Y.; Yonemoto, M.; Kondo, Y. Org. Lett. 2012, 14, 2622. (e) Xia, X.-F.; Wang, N.; Zhang, L.-L.; Song, X.-R.; Liu, X.-Y.; Liang, Y.-M. J. Org. Chem. 2012, 77, 9163. (f) Song, W.; Ackermann, L. Chem. Commun. 2013, 49, 6638. Most previous efforts, however, have focused on indole annulation alone. The efficiency of the synthesis can be increased significantly if the event of indole annulation is coupled with other transformations in a cascade manner. For example, a tandem indole annulation/(4+3) cycloaddition for the construction of both indole and a seven-membered ring simultaneously in the synthesis of cyclohepta[b]indoles is described in the literature. Shu, D.; Song, W.; Li, X.; Tang, W. Angew. Chem. Int. Ed., 2013, 52, 3237. For a synthesis of cyclohepta[b]indoles by a different type of (4+3) cycloaddition, see: Han, X.; Li, H.; Hughes, R. P.; Wu, J. Angew. Chem. Int. Ed. 2012, 51, 10390. Diindolylmethanes are not only present in natural products such as malassezin but also important precursors for other naturally occurring heterocycles such as indolocarbazoles 2 and 3a-3f: Wille, G.; Mayser, P.; Thoma, W.; Monsees, T.; Baumgart, A.; Schmitz, H. J.; Schrenk, D.; Polborn, K.; Steglich, W. Bioorg. Med. Chem. 2001, 9, 955. Kramer, H. J.; Podobinska, M.; Bartsch, A.; Battmann, A.; Thoma, W.; Bernd, A.; Kummer, W.; Irlinger, B.; Steglich, W.; Mayser, P. Chembiochem 2005, 6, 860. Wahlstrom, N.; Romero, I.; Bergman, J. Eur. J. Org. Chem. 2004, 2593. Knolker, H. J.; Reddy, K. R. Chem. Rev. 2002, 102, 4303. Schmidt, A. W.; Reddy, K. R.; Knoelker, H.-J. Chem. Rev. 2012, 112, 3193.

Malassezin, ICZ, and FICZ are potent agonists of aryl hydrocarbon receptor (AhR), which is best known for mediating the toxicity of dioxin and related environmental toxins. Denison, M. S.; Soshilov, A. A.; He, G.; Degroot, D. E.; Zhao, B. Toxicol. Sci. 2011, 124, 1. Recent studies showed that AhR also played a critical role in immune cell differentiation, promoting intestinal immune function, and the development of the prostate. See Quintana, F. J.; Basso, A. S.; Iglesias, A. H.; Korn, T.; Farez, M. F.; Bettelli, E.; Caccamo, M.; Oukka, M.; Weiner, H. L. Nature 2008, 453, 65. (b) Stevens, E. A.; Mezrich, J. D.; Bradfield, C. A. Immunology 2009, 127, 299; Li, Y.; Innocentin, S.; Withers, D. R.; Roberts, N. A.; Gallagher, A. R.; Grigorieva, E. F.; Wilhelm, C.; Veldhoen, M. Cell 2011, 147, 629; Kiss, E. A.; Vonarbourg, C.; Kopfmann, S.; Hobeika, E.; Finke, D.; Esser, C.; Diefenbach, A. Science 2011, 334, 1561; and Mehta, V.; Vezina, C. M. Differentiation 2011, 82, 211, respectively.
It has been demonstrated that selective AhR modulators inhibit prostate tumor metastasis and have anti-asthmatic effects in animal models. Indolo[3,2-b]carbazoles are also important class of organic electroluminescent compounds. See Fritz, W. A.; Lin, T.-M.; Safe, S.; Moore, R. W.; Peterson, R. E. Biochem. Pharmacol. 2009, 77, 1151; Jeong, K.-T.; Hwang, S.-J.; Oh, G.-S.; Park, J.-H. Int. Immunopharmacol. 2012, 13, 377; Gu, R.; Robeyns, K.; Van Meervelt, L.; Toppet, S.; Dehaen, W. Org. Biomol. Chem. 2008, 6, 2484; and Boudreault, P. L. T.; Wakim, S.; Tang, M. L.; Tao, Y.; Bao, Z. A.; Leclerc, M. J. Mater. Chem. 2009, 19, 2921.
Rearrangement of the symmetrical 3,3′-diindolylmethanes to 2,3-diindolylmethanes could be realized using iodine as the catalyst. Gu, R.; Hameurlaine, A.; Dehaen, W. Synlett 2006, 1535. Gu, R.; Hameurlaine, A.; Dehaen, W. J. Org. Chem. 2007, 72, 7207. Low yields, however, were observed when substituted indoles were employed as the substrates. Synthesis of non-symmetric 2,3-diindolylmethanes requires the joining of two different indoles in multiple steps. Tholander, J.; Bergman, J. Tetrahedron Lett. 1998, 39, 1619. Tholander, J.; Bergman, J. Tetrahedron 1999, 55, 6243. Wahlstrom, N.; Stensland, B.; Bergman, J. Synthesis 2004, 1187.